The present invention relates to mooring systems and more particularly concerns a mooring system that provides positive controlled restraint of the position of a moored facility.
In an offshore receiving terminal adapted to receive cargo from a transporting vessel and to transfer the received cargo to onshore facilities, the transport vessel must be moored to the terminal during cargo transfer and must be maintained in position and restrained relative to the terminal facility to allow connection and operation of cargo transfer piping systems and the like. Similar open sea mooring of a vessel is employed at surface facilities above underwater oil/gas producing wells and at other floating terminal or storage facilities. Such mooring systems presently use groups of hausers interconnecting the vessel to anchors or other devices at the ocean bottom. Single point mooring systems have been provided in the form of rigid towers anchored or pivoted to the ocean bottom and rising above the water surface for connection with a vessel which thus may at times be free to swing in a full circle about the mooring point.
Flexible hausers provide insufficient restraint, particularly in storms and highly disturbed sea states. Many such flexible mooring lines are required for control of position of the moored vessel and all must be connected and disconnected. Rigid connections to a moored vessel are only possible between the vessel and a movable system, such as a floating buoy of the type shown, for example, in U.S. Pat. No. 4,148,107 for Mooring Buoy. In such an arrangement, controlled position of the moored vessel depends upon control of the position of the buoy and this, in turn, is positioned by hausers such as flexible chains of a conventional mooring system. Conventional single point mooring terminals and single anchor leg mooring systems such as shown in U.S. Pat. No. 4,042,990 for Single Point Mooring Terminal and U.S. Pat. No. 3,979,785 for Combined Catenary And Single Anchor Leg Mooring System provide restrained and generally buoyant mooring terminals but these, again, are connected to the vessel to be moored by means of flexible lines which provide inadequate control of the moored vessel in high sea states. When sea forces become too great, many of these systems require disconnection of the vessel from the mooring to avoid damage.
Similar but aggravated problems are presented in the docking of vessels to a relatively fixed offshore floating facility where various combinations of flexible tensioned lines and interposed resilient bumpers and the like have been suggested. These also prove inadequate in the presence of highly disturbed sea states.
Accordingly, it is an object of the present invention to provide mooring methods and systems that minimize or eliminate above-mentioned problems.